Experimental Study On Flow Characteristics Of Gas-liquid Two-phase Flow In A Serpentine Tube

In the energy,refrigeration,petrochemical and other industries,the serpentine tube has a wide range of applications as a basic flow and heat exchange element.During the design and operation of heat exchange equipment,it is necessary to make a more accurate estimation of the flow state and heat transfer characteristics of the heat exchange elements.Accurate pump design can not only improve the energy efficiency of heat exchange equipment,but also ensure the safe operation of the equipment.At present,the engineering application of the serpentine tube flow heat exchange equipment is very extensive,but due to the complicated flow characteristics of the gas-liquid two-phase flow in the serpentine tube equipment,there are few research results.The flow pattern and pressure drop of the flow are studied.In this paper,the flow pattern and pressure drop of the gas-liquid two-phase flow in the serpentine tube are studied experimentally,and an experimental platform for the air and water two-phase medium flowing in the serpentine tube is built.Through visualization,the flow pattern characteristics of air-water flowing through each straight pipe section and elbow in the serpentine tube are obtained;the pressure change of the gas-liquid two-phase flow in the serpentine tube is obtained by the pressure sensor.The visualization experiment observed the two-phase flow pattern of three flow modes of the serpentine tube in horizontal upward flow,horizontal downward flow and vertical upward flow,which were classified and analyzed.Draw the flow pattern diagram and compare it with the two-phase flow pattern diagram of the corresponding horizontal straight pipe and vertical straight pipe.The flow pattern diagram of the serpentine pipe flowing in the horizontal direction is similar to the flow pattern diagram of the horizontal straight pipe.The boundary area between stratified flow and plug flow in the flow pattern diagram of a pipe is different from that of a horizontal straight pipe.Two transitional flow patterns of wave-stratified flow and bubbly-plug flow are observed in the serpentine tube.The flow pattern of a serpentine tube flowing vertically upward is quite different from the flow pattern of a vertical straight pipe.There is a transition flow pattern of bubbly-plug flow in the serpentine pipe,and the area of agitated flow is much larger than that of the straight pipe.The area of agitated flow in the tube.In the flow pattern experiment,finally,the data of pressure changes in the time domain under different flow patterns are converted into an image of the power spectral density changing with the frequency domain,and then two specified parameters of the power spectral density are given to quantitatively identify the two flow patterns.method.In the serpentine tube pressure drop experiment,different specifications of serpentine tubes are used to calculate the pressure gradient.The influencing factors of the pressure drop gradient of the serpentine tube are studied,and it is found that the pressure drop gradient of the serpentine tube increases with the increase of the gas and liquid flow rates,and increases with the decrease of the inner diameter and the length of the straight tube.When the bending radius increases,the pressure drop gradient of the serpentine tube increases.The pressure drop gradient of the elbow part of the shaped pipe will increase.Using the previous correlations of pressure drop predictions for straight pipes and elbows to predict the straight pipes and elbows of serpentine pipes,the study found that the pressure drop gradient prediction correlations for straight pipes are not applicable to serpentine pipe bends.The part of the straight pipe section between the heads,and Padilla’s correlation formula for predicting the pressure drop of the elbow basically matches the experimental data and can be used.Finally,based on the Padilla formula,a new correlation formula for predicting the pressure drop of the straight section of the serpentine tube is proposed.Synthesizing the pressure drop prediction correlation formula of the straight section of the serpentine tube and the pressure drop prediction correlation formula of the straight section of the serpentine tube,the predictive correlation formula of the overall pressure drop of the serpentine tube is obtained.